Reduction of grain size represents one of the most effective methods for improving the mechanical properties of polycrystalline materials such as metallic alloys. The mechanical properties of magnesium alloys are particularly sensitive to grain size. Depending on the alloy type/composition and application, the formation of fine and preferably uniform grain structure is commonly achieved either by the use of grain refiners during alloy making and other treatments of the liquid alloy, by special casting procedure (eg. high pressure die casting), or by a processing route invoking severe plastic deformation. The use of grain refiners represents the most suitable and most widely applicable method for grain refining of magnesium metal and magnesium alloys.
One of the most effective and most common grain refiners is zirconium. However, the use of this element has been limited to magnesium alloys that do not contain alloying elements such as aluminium or manganese. Accordingly, all magnesium alloys have been classed in two groups: Zr-containing and Zr-free. For the Zr-free alloys, a number of different methods of grain refining have been developed. These include superheating, carbon addition, additions of carbon-bearing particles and some ceramic particles such as Al4C3, AlN, SiC, TiC, CaC2, FeCl3, C2Cl6, CCl4 and also elements such as Y, B, Ce, La, Nd, and Sr. Among these methods, superheating and addition of carbon and carbon-bearing compounds, as well as the use of FeCl3, have found some industrial application. The drawbacks of superheating method are great energy consumption due to very high operating temperatures required and safety issues. Grain refinement using FeCl3 results in the reduction of alloy corrosion resistance. Compounds such as C2Cl6 or CCl4 have also been used, however due to the release of toxic dioxins, the use of these compounds has serious environmental drawbacks. In addition, none of these methods is readily applicable to a wider group of alloys or universally applicable to all magnesium alloys.
Development of alternative and effective grain refiner and an improved method of grain refining applicable to a wider group of magnesium alloys is still needed. Ultimately, universal grain refiner that can effectively grain refine all or most magnesium alloys is required. Grain refiners that have additional beneficial effects on magnesium and its alloys are peritcularly highly desirable and their use would be highly economical.